The Radical movement had its beginnings at a time of tension between the American colonies and Great Britain, with the first Radicals, angry at the state of the House of Commons, drawing on the Leveller tradition and similarly demanding improved parliamentary representation. These earlier concepts of democratic and even egalitarian reform had emerged in the turmoil of the English Civil War and the brief establishment of the republicanCommonwealth of England amongst the vague political grouping known as the Levellers, but with the English Restoration of the monarchy such ideas had been discredited. Although the Glorious Revolution of 1688 had increased parliamentary power with a constitutional monarchy and the union of the parliaments brought England and Scotland together, towards the end of the 18th century the monarch still had considerable influence over the Parliament of Great Britain which itself was dominated by the English aristocracy and by patronage. Candidates for the House of Commons stood as Whigs or Tories, but once elected formed shifting coalitions of interests rather than splitting along party lines. At general elections the vote was restricted to property owners, in constituencies which were out of date and did not reflect the growing importance of manufacturing towns or shifts of population, so that in many rotten borough seats could be bought or were controlled by rich landowners, while major cities remained unrepresented. Discontent with these inequities inspired those individuals who later became known as the "Radical Whigs".

William Beckford fostered early interest in reform in the London area. The "Middlesex radicals" were led by the politician John Wilkes, an opponent of war with the colonies who started his weekly publication The North Briton in 1764 and within two years had been charged with seditious libel and expelled from the House of Commons. The Society for the Defence of the Bill of Rights which he started in 1769 to support his re‐election, developed the belief that every man had the right to vote and "natural reason" enabling him to properly judge political issues. Liberty consisted in frequent elections. For the first time middle‐class radicals obtained the backing of the London "mob". Middlesex and Westminster were among the few parliamentary constituencies with a large and socially diverse electorate including many artisans as well as the middle class and aristocracy, and along with the county association of Yorkshire led by the Reverend Christopher Wyvill were at the forefront of reform activity. The writings of what became known as the "Radical Whigs" had an influence on the American Revolution.

In 1780 a draft programme of reform was drawn up by Charles James Fox and Thomas Brand Hollis, and put forward by a sub‐committee of the electors of Westminster. This included calls for the six points later adopted in the People's Charter (see Chartists below).

The American Revolutionary War ended in humiliating defeat of a policy which King George III had fervently advocated, and in March 1782 the King was forced to appoint an administration led by his opponents which sought to curb Royal patronage. In November 1783 he took his opportunity and used his influence in the House of Lords to defeat a Bill to reform the British East India Company, dismissed the government and appointed William Pitt the Younger as his Prime Minister. Pitt had previously called for Parliament to begin to reform itself, but he did not press for long for reforms the King did not like. Proposals Pitt made in April 1785 to redistribute seats from the "rotten boroughs" to London and the counties were defeated in the House of Commons by 248 votes to 174.

Popular Radicals were quick to go further than Paine, with Newcastle schoolmaster Thomas Spence demanding land nationalisation to redistribute wealth in a penny periodical he called Pig's Meat in a reference to Edmund Burke's phrase "swinish multitude". Radical organisations sprang up, such as the London Corresponding Society of artisans formed in January 1792 under the leadership of the shoemaker Thomas Hardy to call for the vote. One such was the ScottishFriends of the People society which in October 1793 held a British Convention in Edinburgh with delegates from some of the English corresponding societies. They issued a manifesto demanding universal male suffrage with annual elections and expressing their support for the principles of the French Revolution. The numbers involved in these movements were small, and most wanted reform rather than revolution, but for the first time working men were organising for political change.

The government reacted harshly, imprisoning leading Scottish radicals, temporarily suspending habeas corpus in England and passing the Seditious Meetings Act 1795 which meant that a license was needed for any meeting in a public place consisting of fifty or more people. Throughout the Napoleonic Wars the government took extensive stern measures against feared domestic unrest. The corresponding societies ended, but some radicals continued in secret, with Irish sympathisers in particular forming secret societies to overturn the government and encourage mutinies. In 1812 Major John Cartwright formed the first Hampden Club, named after the English Civil War Parliamentary leader John Hampden, aiming to bring together middle class moderates and lower class radicals.

After the Napoleonic Wars, the Corn laws (in force between 1815 and 1846) and bad harvests fostered discontent. The publications of William Cobbett were influential, and at political meetings speakers like Henry Hunt complained that only three men in a hundred had the vote. Writers like the radicals William Hone and Thomas Jonathan Wooler spread dissent with publications such as The Black Dwarf in defiance of a series of government acts to curb circulation of political literature. Radical riots in 1816 and 1817 were followed by the Peterloo massacre of 1819 publicised by Richard Carlile who then continued to fight for press freedom from prison. The Six Acts of 1819 limited the right to demonstrate or hold public meetings. In Scotland agitation over three years culminated in an attempted general strike and abortive workers' uprising crushed by government troops in the "Radical War" of 1820. Magistrates powers were increased to crush demonstrations by manufacturers and action by radical Luddites.

Economic conditions improved after 1821 and the United Kingdom government made economic and criminal law improvements, abandoning policies of repression. In 1823 Jeremy Bentham co‐founded the Westminster Review with James Mill as a journal for "philosophical radicals", setting out the utilitarian philosophy that right actions were to be measured in proportion to the greatest good they achieved for the greatest number. Westminster elected two radicals to Parliament during the 1820s.

The Whigs gained power and despite defeats in the House of Commons and the House of Lords the Reform Act 1832 was put through with the support of public outcry, mass meetings of "political unions" and riots in some cities. This now enfranchised the middle classes, but failed to meet radical demands. The Whigs introduced reforming measures owing much to the ideas of the philosophic radicals, abolishing slavery and in 1834 introducing MalthusianPoor Law reforms which were bitterly opposed by "popular radicals" and writers like Thomas Carlyle. Following the 1832 Reform Act the mainly aristocratic Whigs in the House of Commons were joined by a small number of parliamentary Radicals, as well as an increased number of middle class Whigs. By 1839 they were informally being called "the Liberal party."

From 1836 working class Radicals unified around the Chartist cause of electoral reform expressed in the People's Charter drawn up by six members of Parliament and six from the London Working Men's Association (associated with OweniteUtopian socialism), which called for six points: Universal suffrage, equal‐sized electoral districts, secret ballot, an end to property qualification for Parliament, pay for Members of Parliament and Annual Parliaments. Chartists also expressed economic grievances, but their mass demonstrations and petitions to parliament were unsuccessful.

Despite initial disagreements, after their failure their cause was taken up by the middle class Anti-Corn Law League founded by Richard Cobden and John Bright in 1839 to oppose duties on imported grain which raised the price of food and so helped landowners at the expense of ordinary people.

When the Liberal government led by Lord Russell and William Ewart Gladstone introduced a modest bill for parliamentary reform, it was defeated by both Tories and reform Liberals, forcing the government to resign. The Tories under Lord Derby and Benjamin Disraeli took office, and the new government decided to "dish the Whigs" and "take a leap in the dark" to take the credit for the reform. As a minority government they had to accept radical amendments, and Disraeli's Reform Act 1867 almost doubled the electorate, giving the vote even to working men.

The Radicals, having been strenuous in their efforts on behalf of the working classes, earned a deeply loyal following; British trade unionists from 1874 until 1892, upon being elected to Parliament, never considered themselves to be anything other than Radicals, and were labeled Lib-Lab candidates. Radical trade unionists formed the basis for what later became the Labour Party.

Following the Napoleonic Wars and until 1848, it was illegal, technically, to advocate republicanism openly. Republicans therefore tended to call themselves "radicals" and the term came to mean a republican (who, by definition, supported universal manhood suffrage). From 1869, a faction, led by Georges Clemenceau, calling themselves Radicals claimed to be the true heirs of the French revolutionary tradition and drifted away from the moderate republicanism of Léon Gambetta. At Montmartre in 1881 they put forward a programme of broad social reforms. At that time, Radicals located themselves on the far left of the political board, opposed to the "Republican opportunists" (Gambetta), the liberal Orléanists, the Legitimists (both monarchist factions) and the Bonapartists.

Radicalism had played a pivotal role in the birth and development of parliamentarism and the construction of the modern Serbian state leading to the Yugoslavian unification. The People's Radical Party formed in 1881 was the strongest political party and was in power in the Kingdom of Serbia more than all others together. The 1888 Constitution of the Kingdom of Serbia that defined it as an independent nation and formalised parliamentary democracy was among the most advanced in the entire world, due to Radical contribution, it's known as The Radical Constitution. In 1902 a crack had occurred in which the Independent Radical Party left and "the Olde" remained in the party, leading it to its considerable downfall and veering into conservatism. In the Yugoslavian kingdom, the Independent Radicals united with the rest of the Serbian opposition and the liberal and civic groups in the rest of the new country and formed the Yugoslav Democratic Party as the central, while several Republican dissidents formed a Republican Party. The NRS had promoted Serb nationalism and put itself as the defender of Serb national interests. Democrats and Radicals were the dominant political parties, especially since the exclusion of the Communists.

In Montenegro, a People's Party was formed in 1907 as the country's first political party and remained the largest in the period of country's parliamentary history until the Yugoslavian unification. Later a True People's Party was formed, which never got widespread popular support and whose bigger part had joined the original NS, but the difference was not ideological, but opposition and support of the Crown and, sometimes, in foreign relations to Serbia (the clubbists were the crown's dissidents and supporters of the people as well as Serbia as a regional power and brotherly ally; the rightists were generally anti-democratic and autocratic monarchist, and also distrustful to the Serbian government's acts on the national plan).

In some countries the radical tendency is a variant of liberalism. Sometimes it is less doctrinaire and more moderate; other times it is more extreme. In Victorian eraBritain the Radicals were part of the Liberal coalition, but often rebelled when the more traditional Whigs in that coalition resisted democratic reforms. In other countries, these left wing liberals have formed their own radical parties with various names, e.g. in Switzerland and Germany (the Freisinn), Bulgaria, Denmark, Italy, Spain and the Netherlands[1] but also Argentina, Chile and Paraguay.[2] This does not mean that all radical parties were formed by left wing liberals. In the French political literature it is normal to make a clear separation between liberalism and radicalism in France. In Serbia both radicalism and liberalism have had their distinctiveness during the 19th century, with the Radical Party being the dominant political party throughout the entire multi-parliamentary period before the unification of Yugoslavia. It had cracked in 1903 when the Independent Radical Party had left, leaving the old People's Radical Party straying far from liberalism and into right-wing nationalism and conservatism. The Independents had created the Democratic Party, whereas the Radicals of today are a far-right political group.

But even the French radicals were aligned to the international liberal movement in the first half of the twentieth century (founded on August 29, 1924[3] and dissolved in 1934),[4] in the Entente Internationale des Partis Radicaux et des Partis Démocratiques similaires.[5]